System for monitoring and controlling the power of a radio frequency (RF) signal in a short-range RF transmitter

ABSTRACT

A system for monitoring and controlling the power of a Radio Frequency (RF) signal in a short-range RF transmitter. An RF signal-generation unit generates the RF signal. A power amplifier amplifies the RF signal. An impedance-matching network matches the output impedance of the power amplifier to input impedance of an antenna. One or more RF power monitors monitor the voltage amplitude of the RF signal at the output of at least one of the RF signal-generation unit, the power amplifier and the impedance-matching network. The one or more RF power monitors further generate at least one alarm signal, based on the voltage amplitude of the RF signal. A control unit modifies at least one operating parameter of at least one of the RF signal-generation unit and the power amplifier, based on the at least one alarm signal generated by the one or more RF power monitors.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/054,124, entitled “SYSTEM FOR MONITORING AND CONTROLLING THE POWER OFA RADIO FREQUENCY (RF) SIGNAL IN A SHORT-RANGE RF TRANSMITTER,” filed onJan. 14, 2011, which is a National Stage Entry under 37 C.F.R. §371 ofPCT/IB2008/054159, filed Jul. 17, 2008, the disclosures of which arehereby expressly incorporated by reference in their entirety.

DESCRIPTION

1. Field of the Invention

The present invention relates to the field of Radio Frequency (RF)transmission. More specifically, the present invention relates to asystem for monitoring and controlling the power of an RF signal in ashort-range RF transmitter.

2. Background of the Invention

A short-range Radio Frequency (RF) transmitter comprises an RFsignal-generation unit, a power amplifier, an impedance-matchingnetwork, a control unit and an antenna. The RF signal-generation unitgenerates an RF signal. The power amplifier amplifies the RF signal. Theantenna radiates the amplified RF signal. The impedance-matching networkmatches the output impedance of the power amplifier to the inputimpedance of the antenna. The control unit controls the operations ofthe RF signal-generation unit and the power amplifier.

If one or more of the RF signal-generation unit, the power amplifier andthe impedance-matching network has failed or malfunctioned, the powerdelivered to the antenna becomes very low. Consequently, the required RFpower to ensure the radio link may not be radiated.

There already exists a system that solves this problem to some extent.The system detects faulty conditions, such as low transmitted power andhigh reflected power to rapidly switch off the power amplifier or turnon a backup transmitter. However, the system does not alert the controlunit when the power amplifier or the RF signal-generation unit fails.

SUMMARY OF THE INVENTION

The present invention provides a system for monitoring and controllingthe power of a Radio Frequency (RF) signal in a short range RFtransmitter, a short range communication unit and a communication systemas described in the accompanying claims

Specific embodiments of the invention are set forth in the dependentclaims.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, aspects and embodiments of the invention will bedescribed, by way of example only, with reference to the drawings, inwhich like references indicate similar elements. Elements in the figuresare illustrated for simplicity and clarity and have not necessarily beendrawn to scale.

FIG. 1 schematically shows an example of a short-range Radio Frequency(RF) transmitter comprising a system for monitoring and controlling thepower of an RF signal in a short-range RF transmitter;

FIG. 2 schematically shows an example of an RF signal-generation unit;

FIG. 3 schematically shows an example of an RF power monitor;

FIG. 4(a) schematically shows pre-defined reference voltage, accordingto an example of an embodiment of the invention;

FIG. 4(b) schematically shows pre-defined reference voltages, accordingto an example of another embodiment of the invention; and

FIG. 5 schematically shows an example of a short-range communicationunit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically shows a short-range Radio Frequency (RF)transmitter comprising a system for monitoring and controlling the powerof an RF signal in a short-range RF transmitter. The short-range RFtransmitter comprises an RF signal-generation unit 102, a poweramplifier 104, an antenna 106, an impedance-matching network 108, one ormore RF power monitors such as a power monitor 110 a, a power monitor110 b and a power monitor 110 c, and a control unit 112 such asmicrocontroller. Hereinafter, the control unit and the microcontrollerare used interchangeably in the application.

In this example, the power amplifier 104 is connected to the output ofRF signal-generation unit 102. Impedance-matching network 108 isconnected between power amplifier 104 and antenna 106. The input of RFpower monitor 110 a is connected to the output of RF signal-generationunit 102. Similarly, the input of RF power monitor 110 b is connected tothe output of power amplifier 104. The input of RF power monitor 110 cis connected to the output of impedance-matching network 108. Theoutputs of the one or more power monitors (110 a, 110 b and 110 c) areconnected to control unit 112. Further, control unit 112 is connected toRF signal-generation unit 102 and power amplifier 104.

The example illustrated in FIG. 1 may operated as follows. RFsignal-generation unit 102 generates the RF signal. Power amplifier 104amplifies the RF signal. Impedance-matching network 108 matches theoutput impedance of power amplifier 104 to the input impedance ofantenna 106. Antenna 106 radiates the amplified RF signal. One or moreRF power monitors (110 a, 110 b and 110 c) monitor the voltage amplitudeof the RF signal. Each of one or more RF power monitors (110 a, 110 band 110 c) compares the monitored voltage amplitude with one or morereference voltages such as an upper reference voltage and a lowerreference voltage. When the monitored voltage amplitude reveals afailure condition, one or more power monitors (110 a, 110 b and 110 c)generate at least one alarm signal, based on the comparison The at leastone alarm signal is indicative of the one or more failures of at leastone of RF signal-generation unit 102, power amplifier 104 andimpedance-matching network 108. The one or more failure conditions mayfor example include the voltage amplitude of the RF signal being greaterthan the upper reference voltage or the voltage amplitude of the RFsignal being less than the lower reference voltage.

It will be appreciated that the maximum power is transferred from asource to a load when the output impedance of the source is equal to theinput impedance of the load.

Control unit 112 may modify one or more operating parameters of RFsignal-generation unit 102 and power amplifier 104, based on the atleast one alarm signal. The one or more operating parameters of RFsignal-generation unit 102 may for example be the frequency and/or theamplitude of the RF signal. Whereas the operating parameters of poweramplifier 104 may for example be the gain and the biasing conditions

Thus, transmission of a Radio Frequency (RF) signal in a short-range RFtransmitter in case of a faulty condition can be ensured and the powerof the RF signal be monitored and adjusted if needed,

For example, the voltage amplitude of the RF signal at the output of RFsignal-generation unit 102 may reach a very high or a very low value dueto a failure or a malfunction of RF signal-generation unit 102. RF powermonitor 110 a detects the voltage amplitude, compares it with the upperreference voltage and the lower reference voltage, and generates analarm signal, based on the comparison. If the voltage amplitude isgreater than the upper reference voltage, a “power too high” alarmsignal is generated. If the voltage amplitude is less than the lowerreference voltage, a “power too low” alarm signal is generated. Controlunit 112 modifies the one or more operating parameters of RFsignal-generation unit 102 or power amplifier 104 to reduce the power ofthe RF signal if the “power too high” alarm signal is received andincrease the power of the RF signal if the “power too low” alarm signalis received.

Also, for example, the voltage amplitude of the RF signal at the outputof power amplifier 104 may reach a very high or a very low value due toa failure or a malfunction of power amplifier 104. As described above,RF power monitor 110 b generates a “power too high” alarm signal if thevoltage amplitude is greater than the upper reference voltage and a“power too low” alarm signal if the voltage amplitude is less than thelower reference voltage. Control unit 112 modifies the one or moreoperating parameters of RF signal-generation unit 102 or power amplifier104, based on the alarm signal received.

Furthermore, for example, the voltage amplitude of the RF signal at theoutput of impedance-matching network 108 may reach a very high or a verylow value due to a failure or a malfunction of impedance-matchingnetwork 108. As described above, RF power monitor 110 c generates a“power too high” alarm signal if the voltage amplitude is greater thanthe upper reference voltage, and a “power too low” alarm signal if thevoltage amplitude is less than the lower reference voltage. Control unit112 modifies the one or more operating parameters of RFsignal-generation unit 102 or power amplifier 104, based on the alarmsignal received.

FIG. 2 schematically shows an example of an RF signal-generation unit102. RF signal-generation unit 102 comprises a local oscillator 202 anda synthesizer 204 connected to the output of local oscillator 202.

Local oscillator 202 generates an RF signal. Synthesizer 204 varies atleast one of the amplitude and the frequency of the RF signal, based onthe input received from control unit 112.

For example, when the voltage of the RF signal at the output of RFsignal-generation unit 102 is greater than the upper reference voltageor less than the lower reference voltage, “power too high” alarm signalor “power too low” alarm signal is generated, respectively. RF powermonitor 110 a sends the alarm signal to control unit 112, indicating afaulty condition. In response to the signal, control unit 112 sends acommand to synthesizer 204 for modifying one or more operatingparameters such as the frequency and the amplitude of the RF signal. If“power too low” alarm signal is generated, synthesizer 204 increases thevalues of one or more operating parameters such as the frequency and theamplitude of the RF signal. If “power too high” alarm signal isgenerated, synthesizer 204 decreases the values of one or more operatingparameters such as the frequency and the amplitude of the RF signal.

FIG. 3 schematically shows an example of an RF power monitor such as RFpower monitor 110 a, RF power monitor 110 b and RF power monitor 110 c.The RF power monitor includes a peak detector 302 followed by acomparator 304.

Peak detector 302 generates an alarm, indicating a low RF powercondition. Peak detector 302 detects the amplitude of the RF signal.Comparator 304 compares the detected amplitude of the RF signal with apre-defined reference voltage, and generates the alarm signal if theamplitude of the RF signal is below the pre-defined reference voltage.

It is understood to a person having ordinary skill in the art that theRF power monitor may include one or more comparators.

According to an embodiment of the present invention, the one or morepredefined voltages may be an upper reference voltage and a lowerreference voltage. It is also understood to a person having ordinaryskill in the art that the value of the upper reference voltage and thelower reference voltage may be different for the one or more RF powermonitors such as RF power monitor 110 a, RF power monitor 110 b and RFpower monitor 110 c.

FIG. 4(a) schematically shows an example of a pre-defined referencevoltage. RF power monitor 110 includes a single comparator with apre-defined reference voltage 402 applied to one input terminal. Anotherinput terminal of the comparator is connected to the output terminal ofpeak detector 302.

When the output of peak detector 302 becomes less than pre-definedreference 402, an RF power monitor such as RF power monitor 110generates a “power too low” alarm signal. Control unit 112 receives thealarm signal and modifies the one or more operating parameters of RFsignal-generation unit 102 and/or power amplifier 104.

FIG. 4(b) schematically shows another example of pre-defined referencevoltages. RF power monitor 110 includes two comparators. A lowerreference voltage 404 is applied to an input terminal of a firstcomparator. The other input terminal of the first comparator isconnected to the output of peak detector 302. An Upper reference voltage406 is applied to an input terminal of a second comparator. The otherinput terminal of the second comparator is connected to the output ofpeak detector 302.

When the voltage amplitude of the RF signal at the input of an RF powermonitor such as RF power monitor 110 becomes less than lower referencevoltage 404, RF power monitor 110 generates a “power too low” alarmsignal. Similarly, when the voltage amplitude of the RF signal at theinput of RF power monitor 110 becomes greater than upper referencevoltage 406, RF power monitor 110 generates a “power too high” alarmsignal. Based on the alarm signal generated by RF power monitor 110,control unit 112 modifies one or more operating parameters of RFsignal-generation unit 102 and/or power amplifier 104.

FIG. 5 schematically shows an example of a short-range communicationunit. The short-range communication unit may be employed in a vehicle.The short-range communication unit monitors the pressure andacceleration of one or more tires of the vehicle and transmitsinformation about the pressure and acceleration to a receiver in thevehicle.

The short-range communication unit includes a pressure sensor 502, anaccelerometer 504, RF signal-generation unit 102, power amplifier 104,antenna 106, impedance-matching-network 108, one or more RF powermonitors, such as RF power monitor 110 a, RF power monitor 110 b and RFpower monitor 110 c, and control unit 112 such as a microcontroller.

Power amplifier 104 is connected to the output of RF signal-generationunit 102. Impedance-matching network 108 is connected between poweramplifier 104 and antenna 106. The input of RF power monitor 110 a isconnected to the output of RF signal-generation unit 102. The input ofRF power monitor 110 b is connected to the output of power amplifier104. The input of RF power monitor 110 c is connected to the output ofimpedance-matching network 108. The outputs of the RF power monitors(110 a, 110 b and 110 c) are connected to control unit 112. Further,control unit 112 is connected to RF signal-generation unit 102 and poweramplifier 104. One or more pressure sensors such as pressure sensor 502are employed in one or more tires of the vehicle. The output of pressuresensor 502 is connected to control unit 112. One or more accelerometerssuch as accelerometer 504 are employed in one or more tires of thevehicle. The output of accelerometer 504 is connected to control unit112.

Pressure sensor 502 measures the air pressure inside the tire of thevehicle and sends the pressure information to control unit 112.Accelerometer 504 measures the acceleration and sends the measuredacceleration information to control unit 112. Control unit 112 generatesa telegram based on the measured pressure information and the measuredacceleration information. Based on the telegram, RF signal-generationunit 102 generates an RF signal. Power amplifier 104 amplifies the RFsignal. Impedance-matching network matches the output impedance of poweramplifier 104 to input impedance of antenna 106. Antenna 106 radiatesthe amplified RF signal. The RF signal radiated by antenna 106 isreceived by the receiver located in the vehicle. The receiver extractsthe at least one of the measured pressure and the measured accelerationinformation from the received RF signal and displays the pressure andacceleration value on a display screen located on a dashboard of thevehicle.

A failure or a malfunction of at least one of RF signal-generation unit102, power amplifier 104 and impedance-matching network 108 leads toundesired variations in the voltage amplitude of the RF signal at eachstage. For example, the voltage amplitude of the RF signal may becomegreater than upper reference voltage 406 or less than lower referencevoltage 404, which is not desired. One or more RF power monitors such asRF power monitor 110 a, RF power monitor 110 b and RF power monitor 110c continuously monitor the voltage amplitudes of the RF signal at theoutput of RF signal-generation unit 102, power amplifier 104 andimpedance-matching network 108, respectively. When the voltage amplitudeof the RF signal becomes less than the lower reference voltage, a “powertoo low” alarm signal is generated by the RF power monitor such as RFpower monitor 110 a, RF power monitor 110 b and RF power monitor 110 c.When the voltage amplitude of the RF signal becomes greater than theupper reference voltage, a “power too high” alarm signal is generated bythe RF power monitor such as RF power monitor 110 a, RF power monitor110 b and RF power monitor 110 c. Subsequently, control unit 112modifies one or more operating parameters of at least one of RFsignal-generation unit 102 and power amplifier 104 based on the alarmsignal, to stabilize the amplitude of the RF signal.

The system described above has a number of advantages over the priorart. Various embodiments of the invention provide a system formonitoring and controlling the power of the RF signal in a short-rangetransmitter. The system ensures proper transmission of the RF signal. Afailure or malfunctioning of the RF signal-generation unit, the poweramplifier and the impedance-matching network is detected and correctiveaction is taken by the control unit. Control unit 112 is continuouslyreceives feedback regarding the voltage amplitude of the RF signal atthe output of the RF signal-generation unit, the power amplifier and theimpedance-matching network and correspondingly modifies the operatingparameters to stabilize the RF signal.

In the foregoing specification, the invention has been described withreference to specific examples of embodiments of the invention. It will,however, be evident that various modifications and changes may be madetherein without departing from the broader spirit and scope of theinvention as set forth in the appended claims. For example, theconnections may be a type of connection suitable to transfer signalsfrom or to the respective nodes, units or devices, for example viaintermediate devices. Accordingly, unless implied or stated otherwisethe connections may for example be direct connections or indirectconnections.

However, other modifications, variations and alternatives are alsopossible. The specifications and drawings are, accordingly, to beregarded in an illustrative rather than in a restrictive sense.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The word ‘comprising’ does notexclude the presence of other elements or steps then those listed in aclaim. Furthermore, the words ‘a’ and ‘an’ shall not be construed aslimited to ‘only one’, but instead are used to mean ‘at least one’, anddo not exclude a plurality. The mere fact that certain measures arerecited in mutually different claims does not indicate that acombination of these measures cannot be used to advantage.

Unless stated otherwise, terms such as “first” and “second” are used toarbitrarily distinguish between the elements such terms describe. Thus,these terms are not necessarily intended to indicate temporal or otherprioritization of such elements.

The invention claimed is:
 1. A system for monitoring and controlling aradio frequency (RF) signal in a RF transmitter, the RF transmittercomprising a RF signal generation unit for generating the RF signal anda power amplifier for amplifying the RF signal, the system comprising: aRF power monitoring unit coupled to an output stage of at least onecomponent of the transmitter, for monitoring a power of the RF signaland for generating at least one alarm signal indicating a condition whenthe power meets a predetermined alarm criterion; and a control unitcoupled to the RF power monitoring unit for receiving the alarm signaland coupled to a control input of the RF signal generation unit formodifying a frequency of the RF signal in response to the alarm signal.2. The system as claimed in claim 1, wherein the RF signal generationunit comprises: a local oscillator for generating the RF signal; and asynthesizer for varying the frequency of the RF signal and wherein thecontrol unit is coupled to the synthesizer.
 3. The system as claimed inclaim 1, wherein the RF transmitter includes an impedance matchingnetwork coupled between the power amplifier and an antenna for matchingan output impedance of the power amplifier to an input impedance of theantenna, wherein the RF power monitoring unit is coupled to the outputstage of the impedance matching network.
 4. The system as claimed inclaim 1, wherein the RF power monitoring unit comprises: a peak detectorcircuit for measuring an amplitude of the RF signal at the output stage;and a comparator for comparing the amplitude with at least one referencelevel and generating the alarm signal based on the comparison.
 5. Thesystem as claimed in claim 1, comprising a first comparator forcomparing an amplitude with a lower reference level and generating apower too low signal when the amplitude comes below the lower referencelevel.
 6. The system as claimed in claim 5, wherein the RF powermonitoring unit comprises a second comparator for comparing theamplitude with an upper reference level higher than the lower referencelevel and generating a power too high signal when the amplitude exceedsthe upper reference level.
 7. The system as claimed in claim 6, whereinthe control unit is arranged to modify the frequency to reduce thefrequency of the RF signal in response the power too high signal and/orto modify the frequency to increase the frequency of the RF signal inresponse the power too low signal.
 8. The system as claimed in claim 6,wherein the control unit is arranged to modify the frequency to reducethe frequency of the RF signal in response the power too low signaland/or to modify the frequency to increase the frequency of the RFsignal in response the power too high signal.
 9. The system as claimedin claim 1, wherein the control unit is arranged to restart a telegramtransmission of the RF signal after modifying the frequency.
 10. Acommunication unit, comprising: a power amplifier for amplifying a radiofrequency (RF) signal; a RF power monitoring unit coupled to an inputstage of the power amplifier, for monitoring a power of the RF signaland for generating at least one alarm signal indicating a condition whenthe power meets a predetermined alarm criterion; and a control unitcoupled with to the RF power monitoring unit for receiving the alarmsignal and coupled to a control input of the power amplifier formodifying at least one operating parameter of the power amplifier inresponse to the alarm signal, wherein the control unit is arranged torestart a telegram transmission of the RF signal after modifying theoperating parameter.
 11. The communication unit as claimed in claim 10,further comprising: a pressure sensor for measuring a pressure of atleast one tire of a vehicle; and a microcontroller for generating atelegram for transmission via the RF signal based on the measuredpressure.
 12. The communication unit as claimed in claim 10, furthercomprising: an accelerometer for measuring an acceleration of the atleast one tire of a vehicle; and a microcontroller for generating atelegram for transmission via the RF signal based on the measuredacceleration.
 13. A communication system including the communicationunit as claimed in claim 10 and a receiving unit positioned within ashort range from the communication unit, for receiving the RF signal andextracting data signals from the RF signal.
 14. A communication systemincluding the communication unit as claimed in claim 10 and a receivingunit wirelessly coupled to the communication unit, for receiving the RFsignal.
 15. The communication unit as claimed in claim 10, wherein theoperating parameter comprises at least one of biasing conditions of thepower amplifier and a gain of the power amplifier.
 16. The communicationunit as claimed in claim 10, further comprising: an impedance matchingnetwork coupled between the power amplifier and an antenna for matchingan output impedance of the power amplifier to an input impedance of theantenna, wherein the RF power monitoring unit is coupled to an output ofthe power amplifier and to an input of the impedance matching network.17. The communication unit as claimed in claim 10, further comprising:an impedance matching network coupled between the power amplifier and anantenna for matching an output impedance of the power amplifier to aninput impedance of the antenna, wherein the RF power monitoring unit iscoupled to an output stage of the impedance matching network.
 18. Thecommunication unit as claimed in claim 10, wherein the RF powermonitoring unit comprises: a peak detector circuit for measuring anamplitude of the RF signal at the input stage; and a comparator forcomparing the amplitude with at least one reference level and generatingthe alarm signal based on the comparison.